Control and regulation of boiler operation

Heat Engines & Boilers

Contents

• Hot- and warm water boiler operation controland safety limits

• Domestic heating and hot water generation control • Hot- and warm water boiler operation control

and safety limits- Spray type superheat control- Water level control

• Boiler controls for operation without permanent supervision

• Steam supply system principals• Steam traps

Hot- and warm water boiler operation control Thermal oil boiler control is similar

• In these type of systems there is not phase change only heating up of heat transfer medium happens. Useful heat can be expressed according to following expression.

Quseful = mwater c ( tout – tin )• Heat supply is controlled mainly by two ways:

- In case of quantity control inlet and outlet temperature level constant and mass flow rate of heat transfer medium is modified - In case of quality control inlet and outlet temperature level modified and mass flow rate of heat transfer medium is constant

• Power level control happens generally from outlet temperature of the boiler(Power level control means burning fuel control done generally by fuel inlet quantity control)

Safety limits

• Maximal outlet temperature

• Minimal inlet temperature(in case of non condensing boilers)

• Overpressure limitation

• Heat transfer medium absence limitation

• Minimal flow limitation

Domestic heating system control

Heating water temperature variation

Domestic heating and hot water generation control

Steam generator operation control

• In case of steam generator useful heat can be calculated according to following expression:

Quseful = msteam ( hout – hin )

• Heat demand variation results variation of steam mass flow rate. Mass flow rate variation at constant power level and at constant feed water parameters results outlet enthalpy and outlet pressure variation.

• Power level control happens generally by means of outlet pressure control, because of previously detailed phenomena.(Power level control means burning fuel control done generally by fuel inlet quantity control)

Outlet temperature control • In case of saturated steam outlet temperature is not

needs to be controlled, because outlet temperature is determined by saturation condition.

• But in case of superheated steam generation superheat temperature is affected by load conditions, and several operation parameters, so it needs to be controlled.

• Earlier several methods were used for superheat temperature control,

• but nowadays only spray type superheat control is used.

Spray type superheat control

• Of all the direct contact types, the spray attemperator has proved most satisfactory.

• Water of high purity is injected directed into the superheated steam main or into a mingling chamber.

• The water is sprayed in through a series of nozzles at the throat of a venturi section, forming a fine mist.

• It is quickly vaporized and first mixes with and then cools the superheated steam. The design must include a thermal sleeve to protect the piping from thermal shock caused by water droplets striking the hot surface.

Spray at different locationsfor outlet steam temperature control

at the boiler outlet in between two superheater

Installation of a spray type attemperator

Installation of a spray type attemperator

Typical injector construction of spray type

attemperators

Feed water quantity control

• According to actual evaporated water quantity the same amount of feed water needs to be fed into the boiler.

• Generally water level in the drum is used for this task.

• In case of once-through type boilers it has to be connected with power level control.

Water level sensors

Water quality control

• At any type of water treatment a certain amount of salt is delivered to the boiler with feed water.

• But the steam delivers nearly any salt out from the boiler.

• So salt is accumulated in boiler water. Over a certain concentration it can cause operation troubles e.g. foaming of water, etc.

• So salt concentration needs to be held below a certain concentration level.

• This is solved by letting out some boiler water quantity, which is called slugging or desalination. Fresh feed water will reduce salt concentration

General safety limitations • Maximal outlet pressure is generally limited by

both- electronic and - mechanical way with safety valves

• Maximal outlet temperature• Water level limitation

- minimal more important- maximal less important

• Boiler water quality limitation- salt concentration by means of water conductivity

Boiler operation supervision

• In general case boiler operation is potential danger, so it needs continuous attendance to supervise.

• With fulfilling special requirements boiler can be operated without permanent attendance. But it does not mean without attendance, it means only that supervisor visit needs to be held regularly, and not continuously.

• Special requirement means that boiler has to be protected automatically from all the possible dangerous operation condition

Boiler controls

Shell boilers controls

Condensate monitoring for salt and oil pollution

Boiler and auxiliary controls

Steam supply system principals

Flash steam formation

Flash steam formation

Example for steam trap installation

Float steam trap

Operation of a thermodynamic steam trap

Operation of a bimetal steam trap

Termic steam trap

SummaryYou are already familiar with

• Hot- and warm water boiler operation controland safety limits

• Domestic heating and hot water generation control

• Hot- and warm water boiler operation controland safety limits- Spray type superheat control- Water level control

• Boiler controls for operation without permanent supervision

• Steam supply system principals

• Steam traps

Thank You for Your Attention !